Wear resistant vapor deposited coating, method of coating deposition and applications therefor

ABSTRACT

A low friction top coat over a multilayer metal/ceramic bondcoat provides a conductive substrate, such as a rotary tool, with wear resistance and corrosion resistance. The top coat further provides low friction and anti-stickiness as well as high compressive stress. The high compressive stress provided by the top coat protects against degradation of the tool due to abrasion and torsional and cyclic fatigue. Substrate temperature is strictly controlled during the coating process to preserve the bulk properties of the substrate and the coating. The described coating process is particularly useful when applied to shape memory alloys.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of U.S. Provisional Application No.60/801,142, filed May 17, 2006, the disclosure of which is herebyincorporated by reference in its entirety including all figures, tablesand drawings.

FIELD OF INVENTION

This invention relates to hard, wear resistant coatings vapour depositedover a metallic or non-metallic surface, in particular, the inventionrelates to a coating to be deposited on rotary tools having cuttingedges utilized in industrial, medical and dental cutting, and formscraping, and is more particularly directed to improvements in bladesand rotary cutting instruments.

BACKGROUND OF THE INVENTION

Hard wearing surfaces are in common use in various industries, and suchhard wearing surfaces are frequently obtained by coating the surface ofa tool made of steel or similar metal, or other hard, enduring material,with a layer of hard wearing ceramic substance, such as carbides,nitrides and carbonitrides, or providing a hard microcrystalline diamondcoating. There are known methods for obtaining hard wearing coatings,such as for example, having a coating of diamond particles incombination with a carbide or nitride layer and then filling the gapsbetween the abrasive particles with a softer intermetallic compound.Another known method is vapour deposition of hard-wearing ceramicmaterials from plasma or by utilizing molten ceramic substances. Hardwearing surfaces for use on medical, surgical and dental tools haveadditional requirements, as such surgical and dental tools need to befrequently sterilized, hence medical tools have to be corrosionresistant.

A device for yielding hard ceramic surfaces by cathodic arc plasmadeposition is described in U.S. Pat. No. 4,851,095, issued to M. A.Scobey et al. on Jul. 25, 1989. The apparatus of Scobey et al. utilizesa high intensity ion flux. Vapour deposition of a hard ceramic material,such as titanium or zirconium nitride, on a stainless steel or titaniumsurface by utilizing a molten evaporant and a hollow cathode, isdescribed in U.S. Pat. No. 5,152,774, issued to W. A. Schroeder on Oct.6, 1992. The vapour deposition of Schroeder is conducted at relativelylow temperature, thus the substrate will have lost little of its initialhigh strength properties, however, the requirement of low surfaceroughness of the deposited layer is not addressed by U.S. Pat. No.5,152,774. In U.S. Pat. No. 4,981,756, issued to H. S. Rhandhawa on Jan.1, 1991, a methodis taught to coat surgical tools and instruments bycathodic arc plasma deposition. The ceramic coating obtained by thistechnology is a nitride, carbide or carbonitride of zirconium orhafnium, in a single layer of 3-10 μm thickness. U.S. Pat. No. 4,981,756also refers to various publications describing known equipment forobtaining hard-wearing surfaces by cathodic arc plasma deposition. U.S.Pat. Nos. 5,940,975 and 5,992,268 issued to T. G. Decker et al. on Aug.24, 1999 and Nov. 30, 1999, respectively, teach hard, amorphous diamondcoatings obtained in a single layer on thin metallic blades or similarmetallic strips utilizing filtered cathodic arc plasma generated byvaporizing graphite. It is noted that no interlayer is formed betweenthe blade surface and the deposited amorphous diamond coating.

The grain size of deposits obtained in conventional cathodic plasma arcmethods may range between 0.5 to 10 μm. Any post-deposition heattreatment which may be required to maintain maximum hardness of thesubstrate's core metal, may lead to internal stresses in the coating dueto differences in the grain size, and can eventually lead to abrasion,spalling, crack formation, grain separation, surface fractures, unevenedges and rough surfaces, and the like, which can drastically reduce thewear resistance and durability of surgical instruments and dental tools.None of the above discussed methods are concerned with even grain sizeand surface structure, and low micro-roughness of the vapour depositedhard, ceramic coatings, which have particular importance for dental andsurgical tools, and in other applications where straight, sharp, evenand nick-free edges are essential requirements.

Users desire cutting blades with sharp edges possessing long life andcorrosion resistance. Typically, blades are initially sharpened to forma wedge shaped cutting edge and re-sharpened as needed, except in thecase of razor blades which cannot be re-sharpened. Sharpness of acutting blade is measured in terms of “ultimate tip radius”, which isdifferent depending on the application. For kitchen knives, rotarycutters, and similar cutting instruments, ultimate tip radius may beseveral thousand Angstroms. In agricultural implements incorporatingrotary blades that cut through the soil, axes, and in chisels, thecutting edge radius may be expressed in microns or even in millimetersrather than Angstroms. Shaving razor blades ordinarily have ultimate tipradii of about 1,500 Angstroms or less. This radius usually includes alayer of hard material coating applied to the wedge shaped base materialof the razor blade. A self-sharpening blade having a cutting edge withdifferent hardness and wear resistance on opposite sides of the blades,provided by applying different coating layers on opposite sides of theblade is described in U.S. Pat. No. 6,105,261, issued to Ecer on Aug.22, 2000. This invention provides a solution to the problem of thecutting edge dulling by providing self-sharpening cutting edges withdifferent hardness and wear resistance on opposite sides of the edgewhile both sides have micro-hardness and wear resistance significantlygreater than the substrate metal. Cutting areas are kept sharp longerwith this method especially in such adverse environments as indental/surgical applications, use as saw blades and scrapers and in theconstruction industry. The disadvantage of this approach is that moreintensive wear on one side of the edge leaves the hard layer unsupportedwhich eventually results in a failure of the more brittle hard layer byfracturing. The soft side of the cutting edge has a higher wear ratewhich affects the support of the brittle thin film coating on theopposite side.

Coatings such a TiN, Ti(CN), or (TiAl)N deposited onto the blade edgeregion of a steel knife blade blank by a cathodic arc process withsimultaneous heating and rotation of the blade blank relative to thedeposition sources are described in U.S. Pat. No. 5,724,868, issued toKnudsen et al. The blade edge region may be sharpened or unsharpenedprior to deposition of the coating material. If the blade edge region isunsharpened prior to deposition, it is thereafter sharpened, preferablyon one side only. An improvement of this method was proposed in U.S.Pat. No. 6,656,186, issued to Meckel et al. and includes depositingdifferent coatings with different hardness on both sides of the bladesadjacent to cutting edge. However, in operation the material on thesofter side of the blade suffers greater wear and is not be able tosupport the harder coating on the opposite side of the blade. Further,this method as well as the methods described previously, does notaddress issues of friction and galling properties of the coated surfaceon the cutting tool.

It is known to coat dental tools and surgical instruments with titaniumnitride and titanium, wherein the coating is obtained by conventionalcathodic arc deposition applied to corrosion resistant stainless steelsubstrates. The cutting surfaces of such medical tools need to besmooth, as well as hard-wearing to prevent trapping and retainingmaterials which can be harmful to the patient. Hence, anotherrequirement is that the cutting edges be very straight, sharp andnick-free to avoid damage to the surrounding flesh and skin duringdental or surgical treatment. There are known methods described, whereinthe cutting tips of surgical instruments made of steel have beensand-blasted and then coated with a hard-wearing ceramic composition,however this method can, and is likely to, increase surface roughnessand unevenness, rather than eliminate it. The main disadvantage of thesemethods is that the hard or even superhard coating with micro-hardnessin excess of 20 GPa is deposited on relatively soft substrate surfacemade of steel or other alloy having micro-hardness less than 8 GPa. Thatcreates a so-named egg-shell effect when the failure of the hard andbrittle thin film coating is due to mechanical deformation of underlyingsoft substrate material.

The duplex technology utilizing ionitriding followed by thin filmcoating was developed to improve the wear resistance to bridge themechanical properties between the soft substrate metal and hard coating.This technology however is limited to selective types of steels andmetal alloys due to poor adhesion of the hard coatings to mostionitrided metallic materials.

In U.S. Pat. No. 6,617,057 issued to Gorokhovsky a multilayer cermetcoating is described which employs alternating metal and ceramic layers.This coating architecture provides high hardness and at the same timesecures necessary elasticity and ductility so the brittle hard ceramiclayer will not fail due to bending and deformation of the substrateswhile the tool is in operation. Using the cathodic arc technology tocreate the multilayer coating eliminates the problems of surfaceroughness and increased radius of cutting edge. The coatings producedhave a moderate hardness and wear resistance but exhibit relatively highfriction and high galling properties. These cermet coatings haverelatively higher friction in comparison with carbon diamond like (DLC)and related coatings.

There is a need for a method which can provide a fine grained, hardwearing ceramic surface that has low micro-roughness, sharp even edges,and has a low friction co-efficient and presents anti-gallingproperties. In preferred cases, the coating should also withstandpost-deposition heat treatment without degradation of the coating.

All patents, patent applications, provisional patent applications andpublications referred to or cited herein, are incorporated by referencein their entirety to the extent they are not inconsistent with theteachings of the specification.

SUMMARY OF THE INVENTION

An object of invention is to obtain a stable cutting edge consisting ofmultilayer coating with different architectures on both sides of theblade of a rotary tool. These coatings primarily focus on reduction ofstickiness and friction of the rotary instruments to reduce torsionfatigue when they come in contact with their counterpart. Otherproperties of the surface engineered instruments are dedicated forimprovement of coating toughness, abrasion wear resistance and corrosionresistance.

The coating of the subject invention generally comprises a topwear-resistant low friction anti-galling segment overlaying a bottommultilayer bondcoating cermet segment which accommodates the internalstresses in the top segment and secures the highest toughness of theentire coating system. A hard case can be optionally created on thesurface of the bulk metal substrate under the bondcoating segment byionitriding or carburizing, which reduces the gradient of mechanicalproperties between the hard ceramic coating and the relatively softmetallic substrate. In addition the ionitrided or carburized layerserves as a hard foundation to support the thin low friction top segmentcoating against mechanical deformation of the soft base metal material.The top coating segment comprises of a near amorphous matrix composed ofcarbon, metal doped carbon, hydrogenated carbon having a mixture ofdiamond like and graphite like interatomic bonding. The amorphous matrixcan be optionally filled with nanocrystalline refractory ceramic phasessuch as carbides, nitrides, suicides, borides, oxides, carbo-borides anda like compounds with size of the crystals ranging from 0.5 to 100 nm.The coefficient of friction of the top segment coating is less than 0.3.The bottom multilayer cermet coating segment has a fine columnarstructure which contributes to the extremely high adhesion and flexuralrigidity while the top layer reduces friction and galling forces andcontributes to the high wear resistance of the coating. This coatingarchitecture is especially beneficial for rotary instruments forprotection against abrasive wear, reducing torsional friction, andimproving fatigue life. This not only improves the durability of theinstrument, but also reduces the negative effect of cutting oncounterparts, which is especially important in the case of dental andmedical instruments. A cutting tool with the coating of this inventionleaves a smooth surface after cutting without holes and disruptionscreated by chunks of materials being removed due to scuffing induced bystickiness of the cutting material to the surface of the cutting tool.

According to one embodiment of the present invention a wear resistant,composite vapour deposited metal ceramic coating is provided on asubstrate capable of electrical conduction. The coating comprises abottom bond segment composed of a metal-ceramic multilayer architectureand a top low friction anti-galling nanostructured segment. The bottombond segment includes at least one metallic layer selected from thegroup consisting of titanium, chromium, vanadium, aluminum, molybdenum,niobium, tungsten, hafnium, zirconium and alloys thereof and having ametallic layer thickness. The bottom bond segment further includes atleast one ceramic layer selected from the group consisting of nitrides,carbides, carbonitrides, oxynitrides, borides, carboborides,borocarbonitrides, silicides, borosilicides and combinations thereof.The bottom bond segment coating has a thickness greater than 0.01 μm, amicro-roughness of less than the total thickness of the uppermostceramic layer, and a micro-hardness in excess of 20 GPa. The top lowfriction anti-galling coating segment includes amorphous diamond likematrix composed of the group of elements consisting of carbon, boron,silicon, nitrogen, hydrogen, oxygen and transition metals optionallyfilled with nanocrystalline refractory ceramic phase embedded in theamorphous matrix. The amorphous matrix can further include diamond-likeinteratomic bonding. The nanocrystalline refractory ceramic phasecomprises carbides, borides, silicates, nitrides and oxides. Thethickness of the top segment coating is greater than 0.01 μm. The sizeof refractory ceramic nanocrystals ranging from 0.5 to 100 nm. Thecoefficient of friction of the top coating segment is less than 0.3.

The substrate can be of steel or titanium alloys. The steel substrate ispreferably made from high chromium steel such as, for example, 440series and 17-4 series. The substrates made of titanium alloys includeNickel-Titanium based alloys. The steel can have an ion nitrided, ionimplanted, oxi-nitrided or carburized surface layer between it and thebottom bond coating segment.

A process is provided for producing a wear resistant, low friction,composite vapour deposited metal-ceramic coating on the surface of thesubstrate capable of electrical conduction. The surface of a substrateis first cleaned then placed into the vacuum chamber of a vapordepositing device capable of providing controlled electric and magneticfields where the substrate is coated with at least one metallic layerand at least one ceramic layer then coated with a top coat. Optionally,the surface of the substrate is treated in a ionitriding, oxy-nitriding,ion implantation or carburizing process step. The process comprises thefollowing steps:

-   -   i) providing a substrate capable of electrical conduction,        having a surface and cleaning said surface with at least one        cleaning method selected from the group consisting of chemical        cleaning, electrolytic cleaning, grinding, polishing, tumbling        and ion bombardment to produce a cleaned substrate;    -   ii) placing said cleaned substrate into the vacuum chamber of a        vapour depositing device capable of providing controlled        electric and magnetic fields, and having a substrate holder        capable of holding at least one substrate, a target electrode        holder, and an inlet for a vapour depositing atmosphere of        controlled composition and pressure;    -   iii) providing a target electrode within said vacuum chamber, of        at least one of the metals selected from the group consisting of        titanium, chromium, vanadium, aluminum, molybdenum, niobium,        tungsten, hafnium, zirconium, and alloys thereof;    -   iv) providing a vapour depositing atmosphere within said vacuum        chamber, comprising at least one of the gases selected from the        group consisting of argon, nitrogen, methane or other        hydrocarbon gas, 3-methylsilane (3MS) gas or oxygen;    -   v) optionally, treating said surface of said substrate in an        ionitriding, oxy-nitriding, ion implantation or carburizing        process step;    -   vi) applying electric potential and a filtering magnetic field        in an atmosphere within said vacuum chamber, to obtain a first,        vapour deposited metal layer selected from the group consisting        of titanium, chromium, vanadium, aluminum, molybdenum, niobium,        tungsten, hafnium, zirconium, and alloys thereof, on said        surface of said substrate;    -   vii) applying electric potential and a filtering magnetic field        in an atmosphere within said vacuum chamber, containing at least        one of the gases selected from the group consisting of nitrogen,        methane or other hydrocarbon gas, 3MS gas or oxygen, to obtain a        second, vapour deposited layer of a ceramic compound of a metal        selected from the group consisting of titanium, chromium,        vanadium, aluminum, molybdenum, niobium, tungsten, hafnium,        zirconium, and alloys thereof, on said first layer deposited on        said surface of said substrate;    -   viii) repeating steps vi) and vii), thereby obtaining multiple        vapour deposited metal layers and multiple vapour deposited        ceramic compound layers on said surface of said substrate;    -   ix) applying electric potential and a filtering magnetic field        in an atmosphere within said vacuum chamber, containing at least        one of the gases selected from the group consisting of methane        or other hydrocarbon, or 3MS gas to obtain a top low friction        vapour deposited segment coating containing metal components        selected from the group consisting of titanium, chromium,        vanadium, aluminum, molybdenum, niobium, tungsten, hafnium,        zirconium, and alloys thereof, and carbon based DLC layers;    -   x) removing said substrate having multiple vapour deposited        metal and ceramic layers on said substrate surface, from said        vapour depositing device; and    -   xi) optionally, heat treating the obtained metal and ceramic        vapour deposited coating layers and a low friction vapor        deposited top layer on said substrate surface.

Alternatively, a blank (unsharpened) substrate can be coated with acermet bondcoating segment, then sharpened. The sharpened surface isthen cleaned and coated with a low-friction, anti-galling top coat. Themethod comprises the steps of:

-   -   i) providing a blank (unsharpened) substrate capable of        electrical conduction by applying at least one finishing method        selected from the group consisting of sandblasting, chemical        cleaning, electrolytic cleaning, grinding, polishing, vibratory        tumbling and ion etching to produce a cleaned substrate;    -   ii) depositing a first hard thin film cermet bondcoating segment        on a blank substrate by vapor deposition process;    -   iii) sharpening the substrate by grinding, cutting, twisting,        and/or polishing for developing at least one side of at least        one cutting edge;    -   iv) cleaning the substrate by applying at least one finishing        method selected from the group consisting of sandblasting,        chemical cleaning, electrolytic cleaning, grinding, polishing,        vibratory tumbling and ion etching to produce a cleaned        substrate;    -   v) depositing a second low friction anti-galling thin film        nanocomposite top coating segment on a top of substrate by vapor        deposition process.

The following optional step can be introduced between step ii) and stepiii); if required or preferred, heat treating the obtained vapourdeposited first segment coating deposited on said substrate surface.

The following additional optional step can be introduced between stepiv) and step v); if required or preferred, ionitriding or ionimplantation prior to deposition of top segment low frictionanti-galling coating layer.

The distinguishing feature of the coating deposition steps, when appliedto the substrates made of thermally sensitive alloys, is that it exposesthe substrate to the plasma deposition in a periodic pulsing manner withdepositing time, when the substrate is exposed to the vapour plasmadeposition process followed by pause time, when plasma environment isremoved from contact with the substrate and the substrate is cooled bymeans of radiation cooling and conduction cooling. The thermal sensitivesubstrates are defined by their sensitivity to being heated to thetemperatures above a certain value critical for this particular alloycausing them to lose some of the important functional properties, whichmay or may not be further restored by subsequent heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the surface engineering device utilizedin this invention.

FIG. 2 is schematic illustration of coating composition modulation:a—multilayer Me/MeN coating architecture; b—modulated coatingarchitecture.

FIG. 3 is a schematic drawing of the cross-section of a rotaryinstrument blade with the coating design having two sides withmultilayer cermet coating.

FIG. 4 is a schematic drawing of a functionally graded coatingarchitecture.

FIG. 5 is a schematic drawing of the low friction, anti-gallingarchitecture including B₄C strengthened diamond-like coating with abondcoating interlayer.

FIG. 6 a is a schematic drawing of an endofile with a duplexionitriding+multilayer coating treatment.

FIG. 6 b is a schematic drawing of an endofile with a duplex coatingssimilar to that shown in FIG. 6 a, but with an ionitrided layer only onthe face side and a multilayer coating on both sides of the flute.

FIG. 7 a is a schematic drawing of the cross-section of an endofile witha dual segment coating architecture including a first multilayer Me/MeNbondcoating segment and a nanocomposite low friction, anti-galling topcoating segment.

FIG. 7 b is a schematic drawing of the cross-section of an endofile witha dual segment coating architecture similar to that shown in FIG. 7 a,but with an ionitrided layer under the bond coating cermet layer.

FIG. 8 a is a schematic drawing of the cross-section of an endofile withthe coating, having a bondcoating multilayer cermet bottom segment onthe outer side of the flute and a low friction, B₄C strengthened carbonDLC in the top segment overlaying the entire flute.

FIG. 8 b is a schematic drawing of the cross-section of an endofile withthe coating similar to that shown in FIG. 8 a, but with the duplexbottom segment coating on the outer side of the flute.

FIG. 8 c is a schematic drawing of the cross-section of an endofile witha coating similar to that shown in FIG. 8 b, but with a duplex bottomsegment coating on the inner side of the flute.

FIG. 9 is a set of NiTi endofiles installed into a substrate holdercopper block with a thermal sink compound shown with or without asurrounding metal cage which absorbs ion energy.

FIG. 10 is a schematic drawing of the different cross sections (a-c) ofthe blade with a duplex coating on one side and a cermet coating on theopposite side of the cutting edge.

FIG. 11 shows a schematic drawings of cross-sections of the rotarydental instrument throughout all stages of its fabrication (a-d).

A detailed description of the preferred embodiments of the inventionwill follow, illustrated by working examples.

DETAILED DESCRIPTION OF THE INVENTION

For the sake of clarity, definition of what is understood by some of theterminology used in the discussion of the preferred embodiments of thepresent invention is provided below.

“Substrate” is understood to mean a three dimensional body providing thesurface on which the vapour species is deposited. Only a portion of thesurface, usually the surface in the proximity of one end of thesubstrate body, is utilized as the depositing surface, and the other endof the body of the substrate is attached to or is supported by, asubstrate mount or holder. It is preferred that the portion of thesurface on which the deposit is to be obtained, has close to uniformtemperature, while the rest of the substrate may be in a temperaturegradient.

“Plasma” is considered to mean an atmosphere of low pressure and hightemperature, containing a mixture of ionized gases and metal vapor. Notall the gases in the plasma are ionized, but it is usual that thespecies to be deposited is ionized. The components of plasma ofteninclude argon or similar inert gases, both in the atomic state and in anionized state.

“Even surface” in the context of a deposited layer surface is understoodto mean that the average distance between the peaks of the depositedsurface and the valleys of the deposited surface, is small. In otherwords, the micro-roughness of an evenly deposited surface is consideredto be low.

In one embodiment of the present invention multiple layers of acontrolled thickness of a metal and of a hard-wearing ceramic compoundof the same metal, are deposited in successive steps on a conductivesubstrate surface, usually stainless steel, titanium alloy, or otherappropriate metal. It is preferred that at least two pairs of the metallayer and the hard-wearing ceramic layer are deposited on the steelsubstrate. The number of layer pairs constituting the coating may rangefrom 2 to as high as 100 s, depending on the desired coating thickness,and on economic considerations. The bottom bondcoating segment can haveat least one pair of a metal layer and a ceramic layer having a commonmetal ion component. The bottom bondcoating segment can comprise amultiplicity of pairs of metal and ceramic layers having a common metalion component. The composite vapor deposited metal-ceramic coating canbe heat treated subsequent to deposition. The thickness of the bottombond coating segment can range between 0.01 μm and 30 μm. The vapordeposited metal-ceramic coating can comprise a portion of a surface of adental tool, a surgical tool or a cutting tool. The bottom bond coatingsegment can comprise one side of the blade, or both sides, while the toplow friction segment can overlay both sides of the blade. The top coat,low friction layer can be deposited over the multilayer bondcoat. Thethickness of the top low friction anti-galling coating segment can rangebetween 0.01 μm and 30 μm. The total coating thickness can range between0.02 μm and 40 μm.

Several different coating deposition processes either associated withphysical vapor deposition (PVD) or chemical vapor deposition (CVD) orhybrid PVD+CVD technology can be used for deposition of the coating ofthe subject invention. The protective or functional thin coatings ondental and medical instruments are aimed to improve cutting efficiency,durability and bio-compatibility. Conventional CVD technology requireshigh temperature for decomposition of metal-organic, halide orhydrocarbon based precursors, which makes its applications restricted tohigh temperature substrates. Using low pressure plasma assisted CVDprocesses (PACVD) allows for reduced substrate temperatures during thecoating deposition stage, but is still restricted to a limited number ofelemental compositions and coating architectures. PVD processes such asmagnetron sputtering and electron beam evaporation are widely used forcoating deposition on cutting tools. Electron beam PVD technology(EBPVD) can provide a theoretically unlimited evaporation rate of a widevariety of different materials: metals, ceramics, cermets, bothconductive and dielectric materials, but the ionization rate of theEBPVD metal vapor flow is extremely low (<0.1%) which require ion beamassistance to achieve dense coatings with acceptable adhesion and finemicrostructure.

Sputtered multilayer coating stacks using multiple sources within thesame system, are used routinely for industrial manufacturing on anysubstrate that can handle vacuum and plasma exposure. To reduce crosscontamination from one source to another either zoned vessels or othermeans to isolate a source from adjacent neighbors are common. Sputteringin conjunction with a reactive gas can yield a myriad of coatings with awide variety of elemental compositions and architectures. Matrix sputtersource structures using 2 or more part targets are possible that yieldvarious composition combinations simultaneously. The magnetronsputtering process is capable of generating an atomized vapor flow fromtargets having low electrical conductivity. Using a split target ofgraphite or boron carbide with a metal segment made of molybdenum,titanium or other transition metals allows for deposition of Me dopeddiamond-like and boron carbide based coatings. Co-sputtering (2 sourceswith different targets on each) yield variability of composition overthe course of a given process. By having various targets adjacent ororiented at roughly 45° to 90° in respect to the substrate surface andvarying the power to each source separately it is possible to yield notonly different thickness but also different compositions within a thinfilm. The primary issues with sputtering are low productivity (rate ofdeposition) and necessity of using large concentrations of argon as asputtering gas. Low ionization rates on the order of 1-3% in magnetronsputtering flows reduce the intensity of ion bombardment assistanceduring coating deposition processes resulting in coarse coatingmorphology and fair adhesion. To improve coating structure, adhesiontoughness, and functional properties, a number of different processeswere introduced. Unbalanced magnetron methods are successful inattaining higher ionization (up to 10-15%) in comparison to conventionalmagnetron sources but it is still too low for substantial improvement ofcoating density and adhesion. Using recently introduced pulse magnetronsputtering technology allows further increases in the ionization rate,but the drawback of this approach is the reduction in the coatingdeposition rate (productivity). Large pulses can also generate anincreased amount of macroparticles increasing the density of surfacedefects. PACVD, magnetron sputtering and EBPVD processes produce vaporplasma flow with low, near thermal kinetic energy, which can bedetrimental for deposition of coating on substrates composed ofmaterials with low electrical conductivity.

The cathodic arc deposition (CAD) technology can evaporate electricallyconductive (metal like) targets and produce a nearly 100% ionized vaporplasma with kinetic energy of ions ranging from 40 to 200 eV and it doesnot require sputtering gas, but it suffers from large amount ofmacroparticles generated along with vapor plasma from cathodic arc spotslocated at the cathode target surface. This setback of the conventionalCAD technology is overcome by filtered cathodic arc processes, whicheffectively eliminate the macroparticles and yield up to 100% ionizedand atomized metal vapor flow. This filtration can occur by means ofmechanical shutters in the direct path of the plasma to the substratematerials. The filtration can also be accomplished by bending the plasmaflow in one or more bends using magnetic steering coils. In thefollowing a brief and simplified description of this technology will beprovided, however, it should be understood that this is given merely toallow clarification of the process parameters and is not intended as anaccurate scientific description of the mechanisms involved in filteredcathodic arc technology. In cathodic arc technology metal droplets andmetal vapour are generated by applying an arc of high current to anegatively charged target metal in a vacuum chamber. At the same time,high concentrations of electrons are also released from the target metalcathode at high speed. The vacuum chamber, by definition, contains a gasat a low pressure, and it is usual that the gas is fed to the chamber asplasma containing a gas or a gas mixture at high temperature in apartially ionized state. The high speed electrons collide with the gasmolecules, thereby further ionizing the gas molecules, which in turncollide with and ionize the metal droplets and metal vapour. The ionizedgas and the ionized metal vapor and metal droplets proceed towards thenegatively charged substrate also located in the vacuum chamber. Themetal deposits in a layer over the surface of the substrate. When thegas is an inert gas no reaction takes place between the ionized gas andmetal vapour. On the other hand, in the instance of the plasma alsocontaining reactive gases, the ionized gases will react with the metalvapour, forming a deposited ceramic compound layer. In conventionalcathodic arc plasma deposition the vaporized metal droplets in theplasma can vary in size, thus the metal or the ceramic compounddeposited on the substrate is likely to exhibit widely varying grainsizes and surface unevenness.

In a recent modification of plasma technology deposits are obtained byfiltering a cathodic arc source by means of appropriately adjustedmagnetic fields. An example of such a cathodic arc plasma coatingapparatus is described in U.S. Pat. No. 5,435,900 issued to V. I.Gorokhovsky, which is incorporated herein by reference. The operatingpressure of the filtered arc deposition process ranges from 10⁻⁶ torr to10⁻² torr, which overlaps with most of the conventional plasma assistedPVD and low pressure CVD processes. This makes it possible to use thefiltered arc plasma environment as ionization and activation means forhybrid processes utilizing a combination of different conventional PVDand low pressure CVD processes operating in a filtered arc plasmaimmersion environment as it is better described in US Pat. ApplicationPublication No. 2004/0168637 A1 of V. I. Gorokhovsky, which isincorporated herein by reference. The hybrid surface engineering system,based on this approach, which includes conventional unbalanced magnetronsputtering plasma sources, EBPVD evaporation sources, thermalevaporation source, low pressure PACVD plasma source and large area dualfiltered arc depositing (LAFAD) plasma sources, which can be used inpracticing the present invention is shown schematically in FIG. 1. Thearc depositing apparatus 10, contains a main vacuum chamber 6, housing asubstrate platform 1, bearing double or triple rotating satellites 8,which are utilized in supporting substrates providing appropriatedepositing surfaces. Substrate platform 1 is connected to a negativebias voltage power supply for rendering the substrate surfaces receptiveof ions during the deposition process. Two plasma guide chambers 2 and2′ are located on opposing sides of vacuum chamber 6, each enclosing twolarge area dual filtered cathodic arc sources 3, attached to the flangeswithin the plasma guide chamber. Thus the vacuum chamber 6 containsaltogether four cathodic arc sources 3, but only one of those isdescribed in detail. In the preferred arrangement two cathodic arcsources 3 are utilized, located at opposing flanged ends of the plasmaguide chamber 2, each having a metal target electrode 4. The metaltarget 4, is connected to the negative pole of a low voltage highcurrent power supply, thus being capable of generating separate metalvapour jets which converge into metal plasma stream 11. The metal vapourjets are focused and steered by magnetic coils 12 and 13. Deflectingcoils 9 bend and collimate plasma streams 11 to direct the flow towardsthe substrate depositing surfaces. Metal droplets of larger size, andmost of the non-ionized neutral species are trapped on [the] baffles 5,of anode-separators 17. Anode-separators 17, bear[s] a positivepotential relative to the plasma stream and thus repel[s] the positivelycharged ions, urging such ions towards the substrates. Vacuum chamber 6,is equipped with a front door 16, for loading the substrates to becoated. Front door 16, also has view ports and flanges 7, for diagnosticassessment and control of the deposition process. On the perimeter ofthe vacuum chamber, preferably opposite front door 16, is located vacuumpumping system 15, which is not shown in detail. The vacuum chamber 6,also has gas entry ports (not shown), two unbalanced magnetrons 18 and18′ equipped with B₄C targets, two electron beam evaporators 19 and 19′and a thermal evaporator 20. When the deflecting coils are notactivated, the cathodic targets 4, serve as powerful electron emitters,thereby providing high electron currents between the cathodic targetsand auxiliary anodes 14. This arrangement creates a highly ionizedgaseous environment during all stages of the process: ion cleaning, ionnitriding and deposition of coating layers. In addition, some form ofheaters can be connected to the auxiliary anodes 14, to allow thetemperature of the depositing surface of the substrate to be controlledindependently. Metal vapor plasma flow can be effectively interrupted byusing the LAFAD deflecting magnetic field as a magnetic shutter. In apulse filtering mode magnetic deflecting coils are periodically turningon and off. This allows creating a multilayer and/or modulated coatingcomposition with a wide range of the sizes of sublayers.

FIG. 2 a shows the multilayer coating architecture consisting of metalsublayers in turn with ceramic sublayers similar to that of the priorart described in U.S. Pat. No. 6,617,057 issued to V. I. Gorokhovsky,which is incorporated herein by reference. The multilayer bondcoating isshown schematically in FIG. 2 a. by reference numeral 21. The steelsubstrate surface which can have been optionally treated by ionnitriding or oxynitriding, is represented as the bottom section 22. Theexemplified coating comprises two metal-ceramic layer pairs. The firstmetal layer, such as titanium, of the first metal-ceramic pair is shownas 24′ and the third layer, which is of the same metal in the secondpair, is represented as 24″. The second layer which is a ceramic layer,such as for example, titanium carbide, in the first pair is representedby reference numeral 26′ and the fourth layer which is of the samecomposition as the ceramic layer of the first pair, is shown as 26″.This coating architecture can be further improved by reducing thebilayer periods to nanometric size, incorporating nanocomposite cermetstructure into the ceramic sublayers and modulating the content ofselected elements across the coating. One of the ways of making thelaminated coating architecture is by modulating the current of one ofthe primary cathodic arc sources of the LAFAD plasma source resulting ina modulating content of selected elements throughout the coating.

FIG. 2 b shows an example of a TiBC coating with a modulated titaniumcontent, which is deposited by surface engineering system presented inFIG. 1 with a dual filtered arc LAFAD plasma source having two primarycathodic arc sources equipped with titanium evaporating targets and twounbalanced magnetrons equipped with B₄C sputtering targets. Themodulation of Ti content is achieved by magnetic shuttering of LAFADsource by periodically turning ON and OFF the magnetic deflecting coils.Additionally, this mode can be used for precise thermal management ofthe substrate in plasma vapor deposition process as it will be in moredetails described below. It is noted, however, that the apparatus ofFIG. 1 is merely an example of a device utilizing magnetic plasma arcfiltering. Any other high temperature vapour depositing apparatus whichmay and may not be fitted with magnetic plasma arc filtering means canbe employed in practicing the present invention. The operation pressureof the LAFAD plasma source which ranges from 10⁻⁶ torr to 10⁻² torroverlaps with almost all conventional low pressure PVD and PACVD plasmasources. This allows a wide variety of coating architectures andcompositions to be deposited using evaporation targets composed ofdifferent materials as well as different reaction gas precursors in astrongly ionized plasma environment. It is also noted, that thepreferred vapour depositing surface engineering system shown in FIG. 1contains an arrangement with four selected cathodic targets, twomagnetron targets, two EBPVD evaporation crucibles and resistiveevaporation boat however, it is possible to operate the device with onlytwo cathodic targets and/or only one magnetron target and/or only oneEBPVD crucible and/or only one resistive evaporation boat.

The application of magnetic filtering of the cathodic arc streameliminates macroparticles, as well as neutral non-ionized species, andthereby substantially only ionized metal vapor and nano-sized metaldroplets carrying a charge, will reach the substrate. This results indeposit layers of even grain size, and surfaces having very lowmicro-roughness. Such surfaces can be referred to as evenly depositedsurfaces.

The substrate selected for deposition in the present process is aconductive material, such as a metal or a hard-wearing substance havingrelatively high electrical conductivity. It can be chosen from differentgrades of stainless steels or titanium alloys. In one of the preferredembodiments the substrate is stainless steel of the AISI 300, 400 (suchas high chromium 440A, 440B, 440C and 440XH (Carpenter) stainless steel)or 1700 series, such as the 17-4 series. One skilled in the recognizesthe compositions of several of these preferred steels, for example; TRIMRITE—C 0.15/0.30, Mn 1.00, P 0.04, S 0.03, Si 1.00, Cr 13.50/15.00, Ni0.25/1.00, Mo 0.04/1.00, balance Fe; 440F—Se—C 0.95/1.20, Mn 1.25, P0.040, S or Se 0.15 (min.), Si 1.00, Cr 16.00/18.00, Mo 0.60, balanceFe; TRINAMET—type analysis C (max.) 0.30%, Mn (max.)1.00%, P (max.)0.040%, S (max.) 0.03%, Si (max.) 1.00%, Cr12.00 to 14.00%, Mo 1.00 to3.00%, Cu 2.00 to 3.00%, Fe, balance; IRK91 (see U.S. Patent ApplicationPublication No. 2004/0197581) (Sandvik Bioline)—C+N≦0.05, Cr 12.0, Ni9.0, Mo 4.0, Ti 0.9, Al 0.30, Si 0.15, Cu 2.0; 7C27Mo2-C 0.38, Si 0.4,Mn 0.6, P (max.) 0.025, S (max.) 0.01, Cr 13.5, Mo 1.0; 20AP-C 1.0, Si0.2, Mn 0.4, P (max.) 0.03, S 0.05, Cr (max.) 0.10, Ni (max.) 0.10, Mo(max.) 0.03, other Pb 0.2. In another embodiments it is a shape memoryalloy such as NITINOL, ENDONOL, or NiTi alloy composed of variouscompositions of nickel and titanium or equiatomic (50/50 at. %)composition of Nickel and Titanium. It is possible that NiTi steels bedoped with other elements as well, such as, for example, copper.

The coatings and methods of the subject invention are exemplified foruse primarily on endofiles and implant drills. The subject coatings andmethods can be applied to scalers, ultrasonic scalers, and dental bursas well. In preferred embodiments, scalers are made of the followingsteels: 440A, 440C, 440Xh, 440F—Se, 1RK91, 13C26, 4C27Mo2, and 20AP.Both Piezo and magnetostrictive ultrasonic scalers are preferably madeof: the 17-4 family of steels, 13-8, TRIMRITE, TTRINAMET, 420, 1RK91,13C26, 4C27Mo2, 20 AP. Preferred compositions for implant drillsinclude: 17-4 steel and 300 series steel, 1RK91, 13C26, 4C27Mo2, and20AP. Dental burs are preferably carbide-stainless steel with highhardness. It is preferred that endofiles are made of 17-4, 13-8, NiTi,TRIMRITE, TRINAMET 420, 1RK91, 13C26, 4C27Mo2, and 20 AP steels.

The substrate surface to be coated is first cleaned, by a usual cleaningprocesses which can include degreasing, tumbling, grinding, polishing,chemical cleaning, degreasing, electrolytic cleaning, ion bombardment orsimilar conventional cleaning steps which can render the surfacereceptive of the deposited substance.

The cleaned substrate can optionally be ion nitrided, oxi-nitrided orcarburised or subjected to ion implantation to increase the hardness andcorrosion resistance of the substrate surface and possibly furtherimprove adherence of the deposited coating. The ion nitriding or ionimplantation step may be conducted in a separate apparatus, or theuniversal surface engineering system shown on FIG. 1 can be adapted tothe ion nitriding or ion implantation process step. This treatmentcreates a case on the surface of the substrate to be coated preventingagainst the egg-shell effect which can reduce performance of thin filmhard coating deposited on relatively soft substrate. This case isdesigned to accommodate the plastic deformation of relatively softsubstrate.

The substrate having a cleaned, and optionally nitrided depositingsurface, is then placed in the vacuum chamber of a suitable cathode arcplasma depositing device having at least one of plasma vapor depositionmeans, such as described above. The arc cathode targets, magnetrontargets, EBPVD evaporating material, resistive evaporating material andPACVD reactive gaseous precursors are selected for the plasma vapourgeneration, are selected as they are capable of forming low friction,anti-galling, hard, wear and corrosion resistant compounds by vapourdeposition. The metallic and non-metallic elements which are preferredin such compound formation are titanium, chromium, vanadium, molybdenum,aluminum, hafnium, zirconium, niobium, tungsten, their alloys, carbon,boron, silicon, and elements of similar nature. The preferred reactiongaseous precursors are nitrogen, hydrogen, oxygen, hydro-carbon gases,borazin, boron trichloride, trimethylsilane (3MS) and gases of similarnature.

The gas atmosphere in the cathodic arc depositing device is controlledsuch that it can yield either a vapour deposited metal layer or a vapourdeposited ceramic compound layer. The ceramic compounds that havedesired wear resistance, corrosion resistance and hardness are thecarbides, nitrides, carbonitrides, oxycarbides and oxynitrides of theabove listed metals. The plasma for depositing the desired ceramiclayers contains one or more of the following gases: nitrogen, methane orother hydro-carbon gas, borazin, 3MS and oxygen. In the vapourdeposition of layers of the above listed metals only argon, or similarinert gas containing plasma is used. Argon may also be utilized todilute or carry the gases reacting with the metal vapour or metaldeposit, to form the desired ceramic [metal] compounds. The metal andceramic compound combinations suitable for forming hard, wear resistantcoatings by vapour deposition in the present invention, are listed inTable 1 below.

The first metal layer to form a metal-ceramic compound layer pair, isobtained by having one of the metals listed above as cathodic targetmetal. The metal layer is deposited in an inert gas, usually argon, in athickness ranging between 0.01 μm and 0.2 μm. The preferred range is0.01 to 0.1 μm. Usually, the same cathodic target metal is used inobtaining the second, ceramic compound layer of the pair, however, thecathodic plasma arc composition is adjusted to contain the gaseouscomponent required to form the appropriate ceramic [metal] compound. Thethickness of the vapour deposited ceramic compound layer is usuallyselected to be between 0.01 and 2 μm, depending on the design, shape andultimate purpose of the deposited coating on the substrate. Themetal/ceramic multilayer coating has to have a high cohesion toughness,which is often determined by resistance to plastic deformation parameterH³/E*², where H is hardness and E is elastic modulus of the coating. Itis required that multilayer coating of this invention has theH³/E*²>0.05.

The multilayer cermet coatings using a ceramic sublayers composed ofnitride, carbonitride, carbide, boride, carbo-boride,carbo-boron-nitrides and combinations thereof can be used as a coatingprotecting against abrasion wear and corrosion as described in U.S. Pat.No. 6,617,057 issued to V. I. Gorokhovsky, which is incorporated hereinby reference. FIG. 3 shows the rotary instrument blade 28 having twosides with multilayer cermet coating 30. Table 1 lists the preferredmetals and alloys used for cathodic targets to obtain the metal layer,and the appropriate layer of ceramic compounds in conjunction with themetal layer. It is to be noted, however, that in some instances, it ispreferred to use two separate metal targets as cathodes, operatedsimultaneously, to obtain the deposited metal alloy layer. For example,it may be convenient to use an aluminum target metal cathode and atitanium target metal cathode operated simultaneously, to obtain anAl—Ti alloy layer.

While the multilayer metal-ceramic coating architecture addresses theabrasion wear resistance and corrosion resistance, there are importantissues which must be addressed in the case of rotary dental instrumentssuch as implant drills and root canal endofiles. In this case thefriction and stickiness between the instrument surface and counterpart(body tissue) creates a large torsional momentum which contributes tothe development of cracks through the surface of the tool and leads toseparation of the instrument. As shown in the U.S. Pat. No. 6,074,209issued to W. B. Johnson, which is incorporated herein by reference,torsional fatigue is the main reason for the failure of rotaryendodontic instruments such as endofiles. When debris sticks to thesurface of the rotary instrument flute it prevents the flute fromremoving the debris from the hole, accumulates a large amount of debrisalong the flute and dramatically increases the torsional momentumimposed on the tool. In addition to reduction of friction and stickinessthe top coating of the subject invention imposes a substantialcompressive stress on the surface layer of the instrument, whichprevents cracks from developing and slows the propagation of the crackseffectively improving the torsional fatigue life of the instrument. Thetop coating of this invention typically provides the compressive stressranging from 0.1 to 8 GPa. The bottom multilayer metal-ceramic coatingsegment protects against both pitting and stress induced corrosion. Theintegrity of this segment is quite important. If the metal surfacefinish is near perfect the pitting and stress corrosion is concentratedthrough the coating defects, imperfections, voids, porosity. The LAFADtechnology substantially reduces the surface defects by effectivelyeliminating the macroparticles and increasing ionization of thedepositing metal-gaseous plasma. Using intense ion bombardment duringvapor plasma deposition process allows not only reduction of the coatingroughness, but also fills and mitigates the initial surface defects viathe increase of adatom mobility and surface diffusivity. FIG. 4 showsthe preferred embodiment of the coating design shown in FIG. 3 whichemploys the functionally graded coating architecture having multilayerMe/MeN based bottom portion (Me means a metallic component which can bechosen from the metals presented in Table 1) followed by transitioncarbonitride interlayer and topped with carbide single layer ormultilayer coating, having an excessive amount of free amorphous carbon.

FIG. 5 shows a blade 32 having a single or multilayer low frictionanti-galling diamond-like coating composed of a mixture of diamond andgraphite bonded atoms. The hydrogen and/or nitrogen can be optionallyadded to this matrix composition to further improve coating toughnessand wear resistance. In a preferred embodiment the diamond-like carbonmatrix is doped by boron, silicon and/or transition metals such as Ti,Al, V, Cr, Mo to form nanocrystalline phases embedded in the carbondiamond-like matrix. The size of nanocrystals ranges from 0.5 to 100 nm.The suitable Me/MeC or Me/MeN/MeCN/MeC bond coating is deposited betweenDLC layer and substrate to secure adhesion of the DLC low frictionanti-galling layer to metal substrate.

FIG. 6 a shows the implant drill 36, made of 300 series stainless steelhaving a duplex treatment: bottom ionitrided case 38 having thickness ofabout 5 μm followed by top multilayer Ti/TiN coating 42 having thicknessof about 1 μm. This coating is deposited in LAFAD surface engineeringsystem shown in FIG. 1. Prior to loading in the LAFAD chamber thesubstrates are subjected to grinding to make a flute followed by mildvibratory tumbling to remove any type of deburrs and defective surfacelayer. The drills are loaded on double rotating satellites of therotating substrate table of the LAFAD chamber. At the beginning of thedeposition process the substrates are heated by means of radiation to300° C. After that ion cleaning is conducted in argon auxiliary arcdischarge plasma at 0.5 mTorr and 250 volts bias. The auxiliary arcdischarge is generated between the primary cathodic arc targets(titanium) of the LAFAD-1 plasma source and auxiliary anode plateinstalled at the back of the LAFAD chamber (FIG. 1) when deflectingfield of the filtered arc source is OFF. After 10 min of ion cleaningthe plasma creating gas is changed to nitrogen and auxiliary arc plasmaimmersion ionitriding process is employed for 10 min to create a thinionitrided case. After that stage the deflecting magnetic field is turnON, the pressure is reduced to 0.3 mTorr, the DC pulse bias voltage isreduced to 40 volts and multilayer Ti/TiN is deposited for 120 min.During the coating deposition stage argon is used for 3 min fordeposition of the Ti sublayer and nitrogen is used for 7 min fordeposition of the TiN sublayer of Ti/TiN multilayer cermet coating.Typical deposition rate of Ti based coating by LAFAD plasma source withdouble rotation is 0.8 μm/hr for Ti metallic sublayer and 0.4 μm/hr forTiN ceramic sublayer layer. This results in a thickness of Ti sublayerin this process of about 30 nm and thickness of TiN sublayer of about 70nm. The total thickness of the coating deposited in this process isabout 1.2 μm.

FIG. 6 b shows the implant drill 36 of FIG. 6 a having a face side ofthe flute ionitrided with ionitrided layer 38 having a thickness ofabout 5 μm and a multilayer titanium nitride 40, having a thickness ofabout 2 μm, overlaying the entire flute. Said ionitrided layer andtitanium nitride layer overlap in the vicinity of the very edge of thecutter. In this fabrication process the drills are subjected to the sameprocedures as that of the previously described regarding FIG. 6 a, butat first the drills are not ground and do not have a flute. After theionitriding stage is completed the drill blanks are cooled, removed fromthe vacuum chamber and subjected to grinding to fabricate the flute.After that the drills are vibratory tumbled for the short time andloaded in the LAFAD chamber for deposition of Ti/TiN multilayer coatingas it is previously described. As a result the duplexionitriding/(Ti/TiN) coating is deposited only on outer side of theflute, not affected by grinding while the inner side of the flute hasonly Ti/TiN multilayer coating deposited on steel substrate without anionitrided case.

FIG. 7 a shows a cross-section of endofile 42 coated with a preferredembodiment of the coating of the subject invention. In this embodiment,the endofile 42 is made of 17-4 stainless steel. The bottom bond coatingsegment 44 is made of multilayer gradient cermet Me/MeN/MeCN/MeC, whereMe element can be taken from transition metals such as Ti, V, Cr, Zr, Alor their combinations (i.e. TiCr, TiZr, TiAl, CrAl, TiV etc.) coatinghaving a thickness of about 100 nm which is followed by low friction topsegment 46 B₄C added carbon DLC layer having thickness of about 250 nm.The bottom segment coating is deposited by LAFAD plasma source withappropriate primary cathodic arc targets (titanium in case of titaniumbased cermet coating) in a process similar to that of previouslydiscussed with the following difference: after deposition of the Ti/TiNnitride multilayer coating portion of the bottom segment coating themethane is added gradually to the nitrogen plasma creating gas todeposit carbonitride sublayer. At the end of deposition of theTi/TiN/TiCN portion of the bottom segment coating the nitrogen iscompletely replaced by methane for deposition of the carbide top portionof the bottom coating segment. Instead of methane the 3MS gas can beused resulting in TiSiCN/TiSiC composition. This composition consists ofSiN amorphous matrix with inclusions of TiC and TiN nanocrystallinephases resulting in superhard properties of this layer. Adding the Si tothe TiCN based composition can be also achieved by using TiSi alloytargets instead of pure titanium targets in primary cathodic arc sourcesof the LAFAD plasma source. After deposition of the bottom segmentcoating the deflection field of the LAFAD plasma source is turn OFF andthe top coating segment is deposited by auxiliary arc plasma immersionmagnetron sputtering process. In this process the plasma creating gas isargon with near 5% methane. The unbalanced magnetrons are turned ON andauxiliary arc discharge is established between primary cathode targetsof the LAFAD source and auxiliary anode plate at the back of LAFADchamber (FIG. 1). The targets of unbalanced magnetron are made ofsintered B₄C ceramic. The DC bias voltage is setup on −50 volts with 100kHz repetition of pulse assistance frequency. The gas pressure isincreased to 0.8-1 mTorr. Sputtering of the B₄C targets in methanecontained strongly ionized plasma immersion environment results indeposition of nanocomposite DLC layer doped with boron contained phasessuch as nanocrystalline boron carbide. The thickness of the top segmentcoating is about 1 μm.

FIG. 7 b shows a cross section of a blade with a preferred embodiment ofa triplex coatings. An ionitrided case 48 5 μm thick is followed by2-segment coating 44, 46 similar to that shown in FIG. 7 a. Fordeposition of this triplex coating architecture the ionitriding inauxiliary arc nitrogen plasma immersion environment is made beforedeposition of the Ti/TiN/TiCN/TiC bottom segment gradient multilayercoating as it is previously described.

FIG. 8 a shows a rotary dental endofile 50 coated with a preferredembodiment of the coating of the subject invention. In this embodiment,the endofile 50 is made of NITINOL or NiTi, the alloy is composed of anear 50/50 at. % of titanium and nickel components. It has a bottom bondsegment coating 52 made of TiCr/TiCrN/TiCrCN/TiCrC multilayer and topanti-friction hydrogen free carbon DLC segment 54. It is achieved bydeposition of DLC on a top of TiCrC bottom segment coating by LAFAD-2filtered arc source equipped with graphite primary cathodic arc targets.During deposition of graphite coatings the substrates are setup up atfloating potential and high voltage 2 kV pulses with width of 25 μs andrepetition frequency of 600 Hz are provided to avoid overheating thetiny endofile substrates. The thickness of the bottom bond coating layerdoes not exceed 20 nm, while thickness of the top DLC segment is about0.25 μm.

FIG. 8 b shows a blade 50 similar to the one shown in FIG. 8 a but madeof martensitic steel, having a cutting edge consisting of two oppositesides. The outer side is subjected to duplex treatment having ionitridedcase 56 of about 5 μm thick followed by Ti/TiN/TiCN/TiC multilayer bondcoating 52, having thickness of about 2-3 μm. The TiBCN nanocompositelow friction anti-galling coating 54 having thickness of about 0.5 μm isdeposited on both sides of the blade overlaying both bottom segment bondcoating 52 on outer side of the blade and uncoated steel surface 58 oninner side of the blade. To produce this coating architecture the blankblade (without the flute) was first subjected to ionitriding followed byTiN—TiCN—TiC multilayer gradient bottom cermet coating depositionprocess, than removed from the chamber and ground to create a flute,which leaves the inner side of the flute uncoated, while outer side ofthe flute (not ground) has duplex coating: 5 μm of ionitrided layerfollowed by 2 μm of the Ti/TiN/TiCN/TiC coating layer. Than thesubstrate is cleaned by mild vibratory tumbling and loaded in the LAFADchamber for the final top segment coating deposited by filtered arcplasma immersion magnetron sputtering process of B4C doped DLC coatingdiscussed in a previous paragraph. The resulting B4C+DLC top coatingsegment having a thickness of about 0.5 μm overlaps both duplex coatedouter side of the flute and uncoated inner side of the flute.

FIG. 8 c shows a blade 50 made of martensitic steel, having a cuttingedge consisting of two opposite sides. In this case the outer side ofthe blade has a 2-segment coating consisting of the bottomTi/TiN/TiCN/TiC multilayer bond coating 52, having thickness of about2-3 μm followed by top TiBCN low friction anti-galling coating havingthickness of about 0.5 μm. The inner side of the blade has duplexcoating consisting of an ionitrided layer 56 having thickness of about 5μm followed by a TiBCN coating segment. The ionitrided layer overlapsthe titanium nitride bottom segment coating layer on the very edge ofthe cutter. The TiBCN nanocomposite low friction anti-galling coating 54having thickness of about 0.5 μm is deposited on both side of the bladeoverlaying both TiN bottom segment coating on outer side of the bladeand ionitrided steel surface on inner side of the blade. To produce thiscoating architecture the blade is first subjected to the bottom cermetcoating deposition process, than subsequently removed from the chamberand grinded to create a flute, which leaves the inner side of the fluteuncoated, while outer side of the flute (not subjected to grinding) has2 μm of the Ti/TiN/TiCN/TiC coating. After this stage the substrate maybe subjected to heat treatment to restore the maximum hardness of thecore metal. After that the substrate is cleaned by mild vibratorytumbling and loaded in the LAFAD chamber for the second subsequentcoating process. At this time the blade is first ionitrided to createionitrided layers on the sides of the blade not covered by TiN coating(the coating was removed during grinding of this side of the flute)followed by deposition of B₄C doped DLC coating by plasma immersionmagnetron sputtering process discussed in a previous paragraph. The TiNbased coating on the outer side of the flute effectively prevents thediffusion of nitrogen into steel because of its outstanding diffusionbarrier properties. In this coating architecture the DLC top coatingsegment is overlaying TiN—TiCN—TiC bond coating on the outer side of theblade and the ionitrided case on inner side of the blade.

FIG. 10 shows different views of a scaler 60 having a core 62 made of440XH martensitic stainless steel and subjected to dual processingtreatment. First, the Ti/TiN multilayer cermet coating 64 havingthickness of about 2 μm is deposited all over the blank blade (beforesharpening). Then the blade is removed from the coating chamber andsharpens resulting in removing the coating from one side of the blade.After sharpening the blade may be heat treated to restore the maximumhardness of the core metal. After that stage the sharpened andoptionally heat treated blade is cleaned by mild vibratory tumbling toremove the very top surface layer which maybe defective or contains someburrs and subjected to plasma immersion ionitrided treatment in lowpressure auxiliary arc nitrogen plasma discharge. Since the coating 64having diffusion barrier properties effectively blocking the nitrogendiffusion, the ionitrided layer 66 is formed only along the side of theblade where the coating was removed after the first coating cycle. FIG.10 c shows a cross-section A-A of the blade 60 shown in FIG. 10 b. Itcan be seen that ionitrided layer forming on front side of the bladeoverlaps the nitride coating layer forming on opposite side of theblade.

FIG. 11 shows the cross sections of an implant drill 68 through alldistinctive stages (a-d) of the surface engineering process producing atriplex coating architecture shown in FIG. 8 c on a rotary dentalinstrument. FIG. 11 a shows the cross-section of the blank drill (beforethe flute is ground) coated with Ti/TiN/TiCN/TiC multilayer gradientcoating 70. FIG. 11 b shows the same tool after grinding which producesa flute. FIG. 1I c shows the drill after the first stage of the secondcoating process, which produces the ionitrided layer 72 on the innerside of the flute, where TiN coating was removed by grinding. FIG. 11 dshows the final product, a triplex coated drill, having the top segmentTBCN low friction anti-galling coating 74, which overlays the TiN on theouter side of the flute and ionitrided layer on the inner side of theflute.

In one of the preferred embodiments, a steel substrate has a bottombondcoating segment of several vapour deposited layer pairs and issubsequently removed from the vacuum chamber of the filtered cathodicarc plasma depositing device and annealed or heat treated in vacuum orin a low pressure inert gas at a temperature between 900° C. and 1100°C. by usual methods, followed by quenching in nitrogen/argon atmosphereand tempering at 150° C. to 400° C. The coated and heat treatedsubstrate then can be sharpened or ground to prepare a necessary cuttingshape blade or flute. After this step, the substrate is cleaned byapplying at least one finishing method selected from the groupconsisting of sandblasting, chemical cleaning, electrolytic cleaning,grinding, polishing, vibratory tumbling and ion etching to produce acleaned substrate. The cleaned substrate the subjected to a subsequentcoating deposition process to apply the overlay low friction,anti-galling coating, which reduces the stickiness between the rotarytool surface and the counterpart. The low friction coating is selectedfrom the group containing carbides, carbo-nitrides, borides, andcarbo-borides with an excessive amount of amorphous carbon forming a DLCtype matrix. It can also be a doped or un-doped DLC layer. Thehydrogenated DLC can be used for further reduction of the friction andstickiness between the instrument and the counterpart.

TABLE 1 Ceramic metal compound layer in combination with the metal,having desired wear Item # Metal Layer resistant properties  1 Ti TiC,TiN, Ti(CN), Ti(OCN)  2 Zr ZrC, ZrN, Zr(CN), Zr(OCN)  3 V VC, VN, V(CN),V(OCN)  4 Cr CrN, CrC, CrCN  5 Hf HfN  6 Mo MoN  7 Nb NbN, NbC  8 W WC 9 Ti-Zr alloy TiZrC, TiZrN, TiZr(CN), TiZr(OCN) 10 Ti-Cr alloy TiCrC,TiCrN, TiCr(CN) 11 V-Ti alloy VTiC, VTiN, VTi(CN) 12 Ti,Mo TiMoN 13Ti,Al TiAlN, TiAlON 14 Ti, Al, Si TiAlSiN 15 Ti, Nb TiNbN 16 Al AlN,Al₂O₃ 17 Ti,Cr (Ti,Cr)B₂ 18 Ti TiB₂ 19 Ti,Al (Ti,Al)B₂

Table 2 lists the preferred metals and alloys used to obtain theappropriate top segment nanostructured coating having low friction andanti-galling properties in conjunction with the bottom bondcoatingsegment.

TABLE 2 Nanocrystalline Elemental Amorphous matrix filling phase Item #composition composition composition 1 C Hydrogen free None single layerDLC 2 C Hydrogen free None multilayer DLC, consisting of iC sublayerswith different ratio of sp3/sp2 bonds and having different hardness 3iCH Hydrogenated DLC None 4 Transition Me doped DLC MeC metal + C 5Ti,B,C Ti, B doped DLC TiC, TiB₂, B₄C 6 Ti,Zr,B,C Ti, Zr, B doped TiC,TiB₂, B₄C, DLC ZrB₂, ZrC 7 B,C B doped DLC B₄C 8 B,C,H B doped B₄Chydrogenated DLC 9 Ti,Al,Cr,Mo, Ti, Al,Cr,Zr,Mo, B TiC, TiB₂, B₄C,ZrCZr,B,C,H doped hydrogenated TiC, (Ti,Al)B₂, DLC (Ti,Cr)B₂, ZrB₂, Mo₂C

The top layer can be also composed of cermet based material doped withlubricious metals such as silver, gold or a like. In this case thecermet provides a wear resistant tough anti-galling matrix with embeddedlubricious metallic inclusions. One example of such coating is TiCN+Ag.Other examples include multiphase nanocrystalline carbides,carbo-nitrides, and borides with addition of silver and/or gold metallicinclusions. Alternatively, the lubricous metal coatings such as silvercan be applied over the bondcoating layer as a replacement for DLC typetop low friction segment, forming Me/MeN+Ag coating architecture.Another alternative solution for the low friction coating segment can besolid lubricant materials such as MoS₂ and WS₂. These solid lubricantcompounds can be embedded into a hard coating matrix either in thebottom bondcoating or top coating segment. One example of such ananocomposite self-lubricating coating is Ti/TiCN multilayer matrix withembedded WS₂ inclusions. This coating can be prepared by hybridLAFAD-UBM process. In this process the LAFAD will be equipped with twotargets made of transition metals such as Ti, Cr, V or a like or theiralloys. The magnetron targets will be WS₂ or MoS₂. The reaction gasatmosphere will be formed by nitrogen or mixture of nitrogen withmethane or other HC gas, while argon will be supplied in the vicinity ofmagnetron targets as a sputtering gas. The resulting coating willconsist of hard cermet matrix with embedded MoS₂ or WS₂ solid lubricantphases.

The preferred substrate surface temperature during the cathodic arcplasma deposition steps is between 100 and 500° C. In some cases thetemperature of the substrates to be coated cannot exceed a certainvalue; otherwise it can have a detrimental effect on the bulk metalproperties. For example, temperature must be controlled in coating ofrotary instruments made of cold work hardening steel such as AISI 300series or NiTi nickel-titanium alloy. In case of instruments made ofAISI 300 series stainless steel the bulk metal properties cannot berestored by appropriate post-deposition heat treatment. In the case ofdental instruments such as endofiles made of NiTi shape memory alloy thetemperature must not exceed 100°-300° C. during the coating process,otherwise post-deposition thermal-mechanical treatments are necessary torestore the shape memory properties of the instrument. In some cases theproperties of the NiTi may not be able to be restored at all if, forexample, the instrument is exposed to too high of a temperature for toolong a period of time. For NiTi type substrates with thin part diametersexposure to temperatures as high as 350° C. or five minutes can degradethe shape memory effect of the material. At 300° C. this loss can occurin 20 minutes, one hour at 250° C., or 2 hours at 200° C. Both thecoating of the substrate material, and post deposition heat treatmentare meant to maintain the stiffness or increase the stiffness propertiesof the substrate when used in many applications. It is also important tonotice that some of the coating layers, specifically the free carboncontained top low friction segment coatings are extremely sensitive tohigh temperature treatment in both oxidizing and reducing environments.Therefore heat treatment of these coatings is as problematic as the bulkmetal substrates. In all these cases precise thermal management of thesubstrate in the vacuum plasma coating deposition process is required.

In a deep vacuum, the only cooling mechanisms are radiation andconduction cooling. Using the pulsing mode of the LAFAD plasma sourcethe precise thermal management of the tiny instruments such as endofilescan be achieved by periodically interrupting the exposure of theinstrument substrate to the vapor plasma environment. This can beaccomplished by using a magnetic shutter which effectively closes thepath of the vapor metal plasma flow toward the substrates to be coated.When the magnetic shutter is closed (the deflection magnetic system OFF)only the near neutral metal vapor flow generated by the EBPVD source ormagnetrons will be deposited on the metal instrument substrate, bringinga negligible amount of heat, while the substrate is losing the thermalenergy by radiation cooling. This allows the temperature of thesubstrate to be controlled during the deposition of the cermet coatingat a desirable level and not to exceed the temperature which damages thebulk metal properties.

The duration time and duty cycle of the filtered arc source operationeffectively determine the substrate temperature in the vacuum plasmadeposition process of the cermet coating, while the total coating timedetermines the coating thickness. The periodic interruption of substrateexposure to metal vapor plasma flow can also be achieved by periodicturning on and off the plasma sources. Since substrate temperature is avery important parameter in determining film properties, specialattention is paid to in-situ monitoring of substrate temperature using ahigh-precision pyrometers and built-in thermocouples.

In addition, the substrate rotary tools such as endofiles are installedinto blocks having a high thermal capacity for heat transfer, theseblocks may be made of copper, aluminum, or similar alloy, then a heatsink paste is used to provide appropriate heat transfer during thecoating deposition process as shown in FIG. 9. If the thermal fluxconveyed by the plasma to the instrument surface is q[W/cm²] and theheat capacity of the tool is C_(t)=c_(t)×m_(t), where c_(t) is specificheat capacity of the metal substrate, m_(t) is mass of the instrument;then the pulse period t_(p), when the instrument can be exposed to thevapor plasma deposition environment can be estimated as following:t _(p)=(C _(t)×(T _(m) −T ₀))/q,  (1)where T₀ is initial temperature of the instrument, which can beestimated as room temperature, T_(m) is maximum temperature to which theinstrument can be heated during vapor plasma deposition treatment. Morethorough calculations must be provided to take in to account theradiation and conduction cooling of the instruments during pause time inthe cycled deposition process. In this case the expression (1) stillgives a first rough estimate of the maximum plasma exposure time. Thetotal coating deposition process time is limited by the heat capacity ofthe substrate holder blocks made of copper, aluminum or other metal withsuitable high thermal conductivity and heat capacity. When thetemperature of substrate holder block T_(b)>(2/3)T_(m) the coatingdeposition process must be interrupted until the temperature of thesubstrate holder block drops below this level.

Another way of trimming the substrate temperature below the valuedetrimental to bulk metal properties, is placing a substrate in ametallic or wire cage, which can effectively reduce the heat of thesubstrate due to intense ion bombardment as illustrated in FIG. 9. It isalso possible to add Hydrogen or Helium gas to the chamber at certainintervals to reduce the chamber and substrate temperatures.

The technology described in this invention can be applied to widevariety of applications in forming and cutting tools, machine parts,medical and dental instruments and many others. In dental instrumentsapplications it can be applied to both handle instruments such asregular and ultrasonic scalers, scalpels, needleholders and to rotatinginstruments such as root canal endofiles, dental drills and burs. Thesubstrate dental instruments can be made of different type of steel andmetal alloys. The preferable type of steel or metal alloy for differentkind of dental instruments is shown in Table 3.

TABLE 3 Description of the metal alloys preferably used for the dentalinstruments of this invention. Name of Preferable type ManufacturerComposition Item dental of steel or metal of substrate of substrate No.instrument alloy metal metal 1 Scalers and 1--440A, 440C, 1-Carpenter440 series is high chromium bearing Currettes 440XH, 440F- 2-Sandvic bysteel; Se; Bioline ™ 440F-Se composition: 2-1RK91, brand 0.95/1.20 C,1.25 Mn, 0.040 P. 13C26, 0.15 S or Se min., 1.00 Si, 4C27Mo2,16.00/18.00 Cr, 0.60 Mo, Bal. Fe 2OAP 2 Ultrasonic 1-17-4 family,2-Sandvic by TrimRite composition: scalers 13-8; Bioline ™ 0.15/0.30 C,1.00 Mn, 0.04 P, 0.03 2-TrimRite, brand S, 1.00 Si, 13.50/15.00 Cr,Trinamet, 420, 0.25/1.00 Ni, 0.40/1.00 Mo, Bal. IRK91, 13C26, Fe;4C27Mo2, Trinamet composition: 20AP, Type Analysis Carbon (Maximum)0.30% Manganese (Maximum) 1.00% Phosphorus (Maximum) 0.040% Sulfur(Maximum) 0.030% Silicon (Maximum) 1.00% Chromium 12.00 to 14.00%Molybdenum 1.00 to 3.00% Copper 2.00 to 3.00% Iron Balance 3 Implant1-17-4 family, 2-Sandvic by 1RK91 composition: drills 300 series;Bioline ™ C + N ≦0.05, Cr 12.0, Ni 9.0, Mo 2-1RK91, brand 4.0, Ti 0.9,Al 0.30, Si 0.15, Cu 13C26, 2.0 4C27Mo2, 20AP 7C27Mo2 composition: C0.38, Si 0.4, Mn 0.6, P max 0.025, S max 0.01, Cr 13.5, Mo 1.0 20APcomposition: C 1.0, Si 0.2, Mn 0.4, P max 0.03, S 0.05, Cr max 0.10, Nimax 0.10, Mo max 0.03, others Pb 0.2 4 Dental burs Cemented Brasseler,carbide Sybron 5 Root canal 1-17-4, 13-8; 3-Sandvic by NiTi shape memoryalloy has near endofiles 2-NiTi Bioline ™ equiatomic 3- TrimRite, brand50%/50% Nickel/Titanium composition Trinamet, 420, 1RK91, 13C26,4C27Mo2,20AP

EXAMPLE 1 Stainless Steel Endofiles with Multilayer GradientTiCr/TiCrN+TiCrCN+TiBC Coating

A set of endofiles made of 17-4 stainless steel were installed into thesubstrate holders positioned on the satellites of the rotating table ofsurface engineering system shown in FIG. 1. The following processparameters were used for the deposition of TiCrN/TiCr—TiCrCN bottomsegment and transitional layer by LAFAD plasma source equipped with two(opposite) Ti and Cr targets. The arc currents were set on approximately100 amperes for both Ti and Cr targets. The auxiliary arc dischargecurrent was set on 150 amperes during argon ion cleaning stage and thenreduced to 40 amperes during coating deposition stage. The substratetemperature did not exceed 300° C. An Advanced Energy Industry MDX-IIpower supply coupled with a Sparkle-V accessory unit was used as a biaspower supply. The bias voltage was set at 250 volts during an ioncleaning stage followed by 1000 volts during 2 mins of a metal ionetching stage. The pulse frequency during ion cleaning/etching stageswas set at 48 kHz with 90% duty cycle (reverse pulse time 2 μs). Thebias voltage during coating deposition stage was set at 60 volts DC. TheTiCrN/TiCr multi-layer nanolaminated coating was deposited at 4×10⁻² Pagas pressure with nitride sublayer being deposited in nitrogen reactiveatmosphere and metallic sublayer being deposited in argon. Each bilayerin TiCrN/TiCr multilayer architecture was deposited during 10 min with 7min dedicated to TiCrN and 3 min to TiCr sublayers. The rotation speedof the substrate platform was set at 9 rpm, which corresponds to a 3-4nm bi-layer thickness in the (Ti based/Cr based) nanolaminatedarchitecture, taking into account an approximately 1.5 μm/hr depositionrate for TiN and 1 μm/hr for CrN coatings deposited in single (one fold)rotation mode. The pure nitrogen was gradually changed to N₂/40% CH₄during a 40 min deposition of the intermediate TiCrCN layer. Thepreliminary set of samples was prepared with a TiCrC upper tribologicalsegment deposited by LAFAD, on top of the transition TiCrCN layer usingacetylene as a reactive gas at pressure of 5 mTorr. During deposition ofthe bottom segment TiCr/TiCrN+TiCrCN coating the magnetic deflectingsystem was set in pulse mode with 50% duty cycle and frequency of 0.1Hz, which result in 5 s deposition time followed by 5 s cooling time ateach bi-period. The thickness of the bottom segment coating was 0.2 μm.Additional samples were produced with an upper layer consisting of TiBCnanocomposite cermet deposited by a hybrid filtered arc-unbalancedmagnetron process. In this case both primary cathodic arc sources ofLAFAD plasma source were equipped with Ti targets for generatingtitanium vapor plasma flow. The magnetron power density was set atapproximately 5.5 W/cm². A small amount of reactive gas (methane) wasadded to argon at a total gas pressure of 0.2 Pa. For deposition ofnanolaminated TiBC/iBC(NL) coating architecture the deflecting magneticfield of the LAFAD plasma source was cycled on for 5 s and off for 25 s.This setting resulted in the TiBC coating architecture consisting ofTiBC sublayer of approximately 4 nm thickness followed by 1 nm of B₄Csublayer per each bi-period across 1 μm of top segment TiBC coating.After the deposition process was finished the substrates were dischargedfrom the chamber. It was found that substrate stainless steel files donot lose their stiffness after the multilayer coating process.

EXAMPLE 2 NiTi Endofiles with Anti-Friction Carbon Diamond-Like Coating

A set of endofiles made of NiTi nickel-titanium alloy were placed in thecopper blocks and installed in the substrate holders, positioned on thesatellites of the rotating table of surface engineering system shown inFIG. 1. The thermal transfer or “thermal sink” compound (“ThermalCompound” Part # 120-8, manufactured by Wakefield Engineering Inc. ofMA) was placed in the hole to reduce the thermal contact resistancebetween the instrument and the copper block so that instruments can beprovided with substantial thermal conduction cooling during vapourplasma deposition process.

The following process parameters were used for the deposition of DLC lowfriction carbon coating using two LAFAD plasma sources, one (forbondcoating layer) equipped with two Ti targets and another one equippedwith two graphite targets. The ion cleaning step was performed in argonionized in auxiliary arc discharge, created between primary cathodes ofone LAFAD plasma source as an emitter of electrons and auxiliary anodesinstalled around the substrate table in a main vacuum chamber. Theauxiliary anode current was 100 amperes, the argon pressure was 0.5mtorr and bias voltage, created autopolarization of substrates under13.56 MHz voltage provided by a RF generator, was 200 volts. The ioncleaning step lasts 2 min, which protects the substrates againstoverheating. After the ion cleaning step the deflecting magnetic fieldof LAFAD source with Ti targets was turned ON for deposition of the bondcoating Ti/TiN/TiC layer. It was started from depositing of the 10 nm Tilayer followed by deposition of 30 to 50 nm of TiN layer in nitrogen andtopped with 100 nm of TiC layer deposited in a methane reactive gasatmosphere. The gas pressure during deposition of the bondcoating is 0.5mTorr, the auto-bias voltage is 50 volts.

After deposition of the bondcoating layer the LAFAD source with Titargets was turned OFF and substrates were subjected to cooling step inhelium or hydrogen at the pressure ranging from 1 to 10 mTorr. Theduration of cooling step ranging from 10 min to 1 hr or more, dependingupon thermal capacity of the substrates to be coated and substrateholder blocks. After the cooling step, the chamber was pumped down to0.01 mTorr and other LAFAD source with graphite targets is turned ON.The 13.56 MHz RF bias power supply was connected to the substrate tableinstead of DC pulse bias power supply, used during deposition of cermetbond coating bottom segment. The substrate auto-bias during this stagewas set at −50 volts. In addition the high voltage pulses having 2.5 kVamplitude, 25 μs width and 600 Hz repetition frequency were appliedsubsequent to the low auto-polarization bias voltage. During the DLCdeposition step the LAFAD deflecting field was periodically turned offfor 10 s and turned on for 5 s which results in the plasma depositionand heating of substrates with subsequent cooling. This approach iscapable of precise thermal management of substrates in vapor plasmadeposition processes. After 1 hr of DLC coating deposition step theLAFAD filter is turned off and substrates are discharged from the vacuumchamber. It is found that with approximately 1 μm of DLC coating theNiTi endofiles fully restored their shape memory, while torsionalfatigue life was improved up to 200% due to reduction of friction andstickiness to the counterbody (bovine). Deposition of the top DLC layerhaving amorphous structure also results in substantial improvement ofcorrosion resistance by effectively filling the holes, voids and otherimperfections and defects both on the substrate surface and in thebottom cermet layer, preventive it against pitting corrosion attacks.

EXAMPLE 3 Endodontic Files Made of 17-4 Stainless Steel with Two SegmentCermet-DLC Coating

A set of blank endofiles made of 17-4 stainless steel is cleaned byvibratory tumbling followed by ultrasonic cleaning dried and then loadedin the surface engineering system shown in FIG. 1. The surface finish ofthe blank endofile after cleaning is better than Rms<20 nm. The firstbondcoating segment consisting of TiZr/TiZrN multilayer+TiZrCNtransition layer+TiZrC top layer is deposited on the blanks. The coatingdeposition process is performed using the LAFAD plasma source with Tiand Zr targets installed into opposite primary cathodic arc sources. Thecoating deposition parameters are largely the same as described beforein Example 1. The coating thickness is 2 μm. After finishing thedeposition of the bondcoating segment the substrates endofiles areremoved from the chamber and subjected to heat treatment to restore thebulk mechanical properties, the primary of which is to retain thehardness and stiffness properties. After heat treatment the coatedblanks are subjected to grinding and polishing treatment to make a flutewith a cutting edge. As a result of this step the outer side of saidflute remains coated with a 2 μm thick bottom bondcoating segment andthe other (inner) side of said flute is uncoated, while the very tip ofthe cutting edge is entirely made of the bondcoating multilayer cermet,having a hardness of H_(—)>25 GPa. This step forms a cutting flute witha metallic underside and a ceramic metal outer layer or top side. Afterthat the instruments are subjected to chemical-mechanical vibratorytumbling which creates a fine surface finish on the uncoated side of theflute and does not affect the outer side of the flute and the very tipof the cutting edge which are much harder than vibratory tumbling media.After that the substrate instruments are ultrasonically cleaned andplaced in the copper blocks positioned on the satellites of the rotatingtable of surface engineering system shown in FIG. 1. The thermaltransfer or “thermal sink” compound (“Thermal Compound” Part # 120-8,manufactured by Wakefield Engineering Inc. of MA) is placed in the holeto reduce the thermal contact resistance between the instrument and thecopper block so that the instruments will have substantial thermalconduction cooling during vapour plasma deposition process. After ioncleaning and 5 min of exposure to TiZr metal vapor plasma in methanereactive gas atmosphere at 1 mtorr and −100V bias for deposition of thinTiZrC sublayer, the LAFAD source deflecting field is turned off andremains in electron emission auxiliary arc mode for ionizing gaseousplasma in the main chamber. At this moment methane flow rate is reducedto 4 sccm, argon is added as a main balance gas to reach 1 mtorroperating pressure, two unbalanced magnetrons with B₄C targets areturned on and high voltage (12 kV) pulse bias is imposed on thesubstrates to provide boron-carbon ion implantation of the uncoated andcoated sizes of the flute. This stage continues for 10 minutes followedby deposition of nanolaminated TiZrBC coating containing large amount offree amorphous carbon by periodically exposing the substrates to TiZrmetal vapor flow when deflection magnetic field of LAFAD source isturned on and continuous exposure of the substrates to B₄C magnetronsputtering flow and additional hydrocarbon plasma flow at −50 voltsbias. This results in deposition of a low friction non-stick TiCrBC topcoating segment, which effectively encapsulates the smooth metallicsurface of the inner side of the flute and provides large improvement offatigue life by securing low torque momentum and preventing thedevelopment and fast propagation of surface microcracks. At the sametime this coating design has demonstrated cutting efficiency byretention of the wear and corrosion resistant low friction anti-gallingdual ceramic cutting edge of the flute. Using 3MS reactive gas inaddition to nitrogen during deposition of the top low friction segmentcoating results in TiCrBSiCN composition which further improves thecorrosion resistance and cutting efficiency of the entire surfaceengineering of this type of dental instruments.

EXAMPLE 4 Endodontic Files Made from NiTi Alloy with 2-SegmentCermet+DLC Coating

In this process the blank endofiles without flutes made of NITINOL or50/50 at % NiTi alloy are subjected to deposition of a relatively thickTiCr/TiCrN/TiCrCN/TiCrC multilayer gradient cermet coating 2 μm thick atthe first stage of the surface engineering process. During deposition ofthe bottom bond coating segment the temperature of the endofilesubstrates can reach up to 500° C., which effectively erases the shapememory properties. After this stage the coated blanks are removed fromthe LAFAD surface engineering chamber and subjected to annealing heattreatment stage. During this stage the coated blank files are subjectedto 30 min heating at 1100° C. in nitrogen (99.995 purity) followed byrapid cooling by immersing the boat with files into ice. After annealingthe coated blank files are subjected to thermal-mechanical treatmentstage consisting of grinding by fine diamond wheels in a multi-stepgrinding-tempering process. Alternatively, after annealing and rapidquench the files can be subjected to tempering at temperatures rangingfrom 400 to 650° C. for time duration ranging from 15 min to 2 hrs.During this process the files are subjected in turn to grinding andtempering in a tempering furnace which allows restoring its shape memoryproperties. After this stage the files, which now have a flute arecleaned by mild vibratory tumbling and loaded second time in the LAFADcoating chamber for the subsequent deposition of hydrogen free DLCcoating. This process is provided by LAFAD plasma source shown in FIG.1, which is equipped with two graphite primary cathodic targets. Thesubstrate endofiles are installed with double rotation capability intocopper blocks with thermal sink compound. No plasma creating gases areused in this process and the chamber pressure during DLC process ismeasured at about 0.01 mtorr. The substrates are subjected to floatingbias potential with superimposed high voltage pulses of 2 kV amplitude,25 μs duration and 1000 Hz repetition frequency. The duration of thisdual filtered arc deposition process is 4o min resulting in depositionof 0.25 μm DLC layer, which overlays the bottom bond coating cermetlayer on the outer side of the flute and uncoated NiTi alloy on theinner side of the flute. The hardness of the DLC layer deposited on NiTialloy was measured by means of nanoindentation as 25 GPa. The cumulativecompressive stress in combined cermet+DLC coating was measured as about3 GPa.

A novel coating is described that protects the coated surface againstwear and corrosion while providing a low friction, anti-galling surface.In the exemplified embodiment, this novel coating architecture of amultilayer metal/ceramic bondcoat topped with a non-friction,anti-galling top coat is applied to rotary tools for dental and medicalapplications. It is important to note however that the subject coatingcan be effectively applied to other dental and surgical instrumentsincluding, but not limited to, saw blades, scalers, curettes, scissors,razorblades, scalpels, orthodontic components, burs, and implants.Additionally, the subject coating and the method of temperature controldescribed for applying the coating are intended to be used for coatingultrasonic cutting, debriement, surgical, and periodontal therapy toolsor instruments both of Piezo and Magneto Restrictive types for dentaland medical applications. Finally the coatings and methods of thesubject invention can be applied to other industries, such as theaerospace industry, the automotive industry (for use on, for example,gears, bearings, combustion engine components such as pistons and pistonrings, valves etc.) and other cutting and forming tools industries (forexample, for use on dies and molds).

It is understood that the foregoing examples are merely illustrative ofthe present invention. Certain modifications of the articles and/ormethods may be made and still achieve the objectives of the invention.Such modifications are contemplated as within the scope of the claimedinvention.

1. A wear resistant, composite vapour deposited coating on a cuttingedge of a substrate comprising: a metal-ceramic coating on the substratecomprising at least two pair of a metallic layer selected from the groupconsisting of titanium, chromium, vanadium, aluminum, molybdenum,niobium, tungsten, hafnium, zirconium, and alloys thereof; overlayed bya ceramic layer selected from the group consisting of nitrides,carbides, oxides, oxycarbides, oxynitrides, borides, carboborides,borocarbonitrides, silicides, borosilicides and combinations thereof,the metal-ceramic coating having a hardness of greater than about 20gigapascals and a toughness of greater than about 0.05 H³/E²; and atleast one top coat overlaying the metal-ceramic coating, the top coatcomprising an amorphous diamond-like matrix selected from the groupconsisting of carbon, silicon, nitrogen, hydrogen, oxygen and transitionmetals the top coat having nanocrystals sized from about 1 to about 100nanometers, and having a friction coefficient of less than 0.3; whereinthe top coat imposes a compressive stress of from about 0.1 to about 8gigapascals.
 2. The coating of claim 1, wherein nanocrystallinerefractory ceramic phases ih said top coat are selected from the groupconsisting of carbides, nitrides, silicides, borides, oxides andcarbo-borides.
 3. The coating of claim 1, wherein said metal-ceramiccoating has at least one pair of a metallic layer and a ceramic layerhaving a common metal ion component.
 4. The coating of claim 1, whereinsaid metal-ceramic coating comprises a plurality of pairs of metalliclayers and ceramic layers having a common metal ion component.
 5. Thecoating of claim 1, wherein said metal-ceramic coating is heat treatedafter deposition.
 6. The coating of claim 1, wherein said metal-ceramiccoating has a thickness of between about 0.01 micrometers and about 30micrometers.
 7. The coating of claim 1, wherein said top coat has athickness of between about 0.01 micrometers and about 30 micrometers. 8.The coating of claim 1, wherein said substrate is treated by a processselected from the group consisting of ionitriding, ion implantation andcarburizing.
 9. The coating of claim 1, wherein said coating has athickness of between about 0.02 micrometers and about 40 micrometers.10. The coating of claim 1, wherein said substrate is Bioline 1RK91stainless steel.
 11. The coating of claim 1, further comprising atransition layer between the metal-ceramic coating and the at least onetop coat.